ARM: dts: msm: replace cobalt with 8998 for msmskunk

Update the code names from pmcobalt and pmicobalt to pm8998 and
pmi8998 respectively.

Change-Id: Icc543e07efef6bb1623cd19c61cbec72be602ef6
CRs-Fixed: 1082230
Signed-off-by: David Collins <collinsd@codeaurora.org>